This invention relates generally to counterpressure bottling machines and more specifically it relates to a filling unit for use in such machines, the unit being of the type having no filling pipe and having a siphon closure arranged at the level of the valve seat in the liquid discharging channel, the siphon closure comprising a ring-shaped groove for sealing liquid and a bell-shaped stopper projecting with its rim portion into the groove.
Filling units of this type are used chiefly for charging CO.sub.2 --containing liquids that are discharged from a pressure tank of the bottling machine through the filling unit into a bottle connected to the latter. Prior to the initiation of the actual filling process, the pressure between the bottle and the pressure tank is equalized so that the liquid is discharged into the bottle by the force of gravity. During the filling process the counterpressure gas taking place in the bottle is exchanged for the discharged liquid and returned into the gas space in the tank. For this purpose a gas-return pipe is used whereby the position of its opening in the bottle determines the level of the charge and limits the rate of the filling process as soon as the liquid reaches the outlet opening and the exchange of the gas from the bottle back into the liquid tank is no longer possible. In known filling units of this type the danger exists that an amount of gas taking place above the liquid level might bubble up through the still open liquid discharging channel and cause a supplemental discharge of the liquid retained above the valve seat in the liquid discharging channel. In order to avoid this shortcoming, it has been devised to make the valve for the liquid in the form of a siphon by providing the valve plunger with a bell-shaped stopper the downwardly projecting bell-like rim portion of which is immersed into sealing liquid retained in a siphon channel. Apart from a minor decrease in efficiency of the filling system, this siphon-like embodiment has the disadvantage that both the annular groove forming the siphon channel and the bell-shaped stopper have to be made relatively long to be deeply covered by the liquid. The reason for this extended structure is that the bell-shaped stopper always moves together with the plunger of the liquid discharging valve between the closing and opening position of the latter. Due to the fact that the siphoning effect is needed mainly in the open position of the valve, the bell-shaped stopper has to be so long that also in this open position it is sufficiently immersed in the sealing liquid in the siphon groove. Another disadvantage of this known embodiment results also from the fact that due to the different depth of immerging of the bell-shaped stopper according to the difference in opening position of the valve, there result variations in the cross-section of the liquid discharging passage and these pg,4 variations in turn case different levels of charge in the bottle. In addition, the continuously changing position of the stopper and the resulting continuous change of boundary layers of the liquid prevent constructional measures that in view of surface tension of the discharged liquid would be desirable for increasing the cross-section of the liquid discharging passage.